Power supply for identification and control of electrical surgical tools

ABSTRACT

An electronic circuit for identifying an electrical surgical tool and for providing a selectable constant current appropriate to the identified electrical surgical tool.

FIELD OF THE INVENTIONS

[0001] The devices described below relate to power supplies intended tosupply electrical power to medical instruments.

BACKGROUND OF THE INVENTIONS

[0002] Many electrical surgical devices are provided in the form ofelectrical surgical tools, such as a thermal cautery device, which canbe plugged into a separate power supply. Typically, the power suppliedto the electrical surgical tool must be carefully controlled; thus, thepower supply includes circuitry to convert available AC power to AC, RF,or DC power at the desired output power levels or frequencies. Forexample, Herzon, Thermal Cautery Surgical Forceps, U.S. Pat. No.6,235,027 (May 22, 2001), shows thermal cautery forceps using a powersupply to deliver a regulated current to the resistive heating elementsin the forceps. Our own cautery instruments, such as the Starion®Thermal Cautery Forceps, which comprise forceps with resistive heatingelements disposed on the grasping tips, are designed to work with ourPowerPack Surgical Power Supply. Currently marketed versions of thispower supply provide a current to the resistive heating elementsdepending on the heat load and temperature of the resistive heatingdevice. In addition to these two devices, many electrical surgicalinstruments are currently marketed to address a variety of surgicaltechniques and the number of surgical instruments available has beengrowing.

[0003] The increase in the variety of surgical instruments hasintroduced a problem in medical-grade power supplies. Most powersupplies can operate with different kinds of medical instruments, aslong as an electrical connection can be established between the powersupply and the instrument. However, a medical device manufactured by onecompany may perform slightly differently than expected when the medicaldevice is used in conjunction with a power supply from another company.Since many medical procedures require precise control of the electricalproperties of the medical device, a surgeon or doctor mayunintentionally harm a patient when the surgeon uses a power supply anda medical device from different manufacturers. For example, though theStarion® PowerPack provides optimal power to the various Starion®electrical surgical tools for which it is intended, the use ofconnectors available to other medical device manufacturers may permituse of non-Starion® electrical surgical tools with the PowerPack. Whenused in combination with such third party electrical surgical tools, itis not possible to ensure that the optimal amount of power is deliveredto the tool. Thus, the tool may not function as desired, with the resultthat the patient may be harmed. Thus, a medical-grade power supply isneeded which operates only with the instruments made by thatmanufacturer and tested with that model of power supply.

SUMMARY

[0004] The methods and devices described below relate to a power supplythat identifies an electrical surgical tool, such as a thermal cauterydevice, and provides power only to electrical surgical tools that areidentified by the power supply. The power supply uses a deviceidentification circuit and a constant current circuit to control thepower output to an electrical surgical tool. The device identificationcircuit identifies whether an electrical surgical tool is designed to beused with that power supply. If the device identification circuitrecognizes the electrical surgical tool, then the constant currentcircuit will provide a constant current, or electrical power, to thetool. In addition, the constant current circuit will provide the toolwith the amount of power required by that particular device. If thedevice identification circuit does not recognize the device connected tothe power supply, then the constant current circuit provides no power tothe device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 illustrates the physical power supply box.

[0006]FIG. 2 is a block diagram of the power supply system.

[0007]FIG. 3 is a block diagram of the power board system.

[0008]FIG. 4 is a circuit diagram of the device identification circuit.

[0009]FIG. 5 is a device identification table showing specific values ofthe identification resistor, the identification voltage, and thecomparator outputs for three distinct thermal cautery devices and aforeign device.

[0010]FIG. 6 is a circuit diagram of the constant current circuit.

[0011]FIG. 7 is a circuit diagram of an alternate device identificationcircuit.

[0012]FIG. 8 is a circuit diagram of an alternate device identificationcircuit with switching.

DETAILED DESCRIPTION OF THE INVENTIONS

[0013]FIG. 1 illustrates a physical power supply box 1. The power supplybox 1 is typically a non-sterile, reusable, AC powered device designedfor use only with certain instruments, medical devices, electrosurgicaldevices, or other electrical surgical tools such as thermal cauterydevices. The power supply is connected to an AC power source. The powersupply has an on-off switch 2, an AC power connector 3, an LED powerindicator 4, a control knob 5, and a hanger 6 suitable for suspendingthe power supply on a support object, such as an IV pole. The powersupply is also equipped with an input 7 for an interface board, controlboard, or switches, and an output 8 to the medical instrument. Thesupply has input requirements of 100 to 240 VAC at 50 to 60 Hz and at80W, has a maximum output of 32 VA, a no load voltage of 5V DC, and isoperated at a duty cycle of about 5 seconds on and 10 seconds off. Theoutput current is in the range of 2.4A to 4.4A, depending on whichinstrument is used and on the output desired by the user.

[0014] One version of the power supply, which is intended for use withcautery instruments, has three output heat levels: low, medium, andhigh. The levels correspond to the desired heat output of the thermalcautery instrument's resistive heating element or elements, andcorrespond to current outputs of the power supply. A tone indicates thelevel of heat being applied to the cautery device. For example, a lowtone indicates a low heat setting, an interrupted low tone indicates amedium heat setting, and high tone indicates a high heat setting. Otherdevices have multiple heating elements and each element may havedifferent heating levels. For medical devices with multiple settings orelements, the various settings and elements are adjustable. Theadjustment of these settings or elements is typically facilitated by aninterface board, or control board, that can switch between power levelsor heating elements.

[0015]FIG. 2 is a block diagram of the power supply system. Block 11 isthe AC power input and is equipped with a power on/off switch 13. The ACpower is connected to an isolated switching DC power supply 12, or AC toDC converter, through switch 13. However, the AC to DC converter can bereplaced with an AC to low frequency AC converter, an AC to highfrequency AC converter, or an AC to low power AC converter. The isolatedswitching DC power supply 12 typically has an output of +5 volts DC. Inaddition, the isolated switching DC power supply is UL rated for heartcontact, meaning that the output of the power supply can directly touchthe patient. The DC power supply 12 is connected to a power board 14which contains a constant current circuit. The power board 14 is alsoconnected to the electrical surgical tool 15, a power LED 16 indicatingwhether the power supply is “on”, and an interface or control board 17.The interface board contains a device identification circuit and acontrol voltage circuit. The interface board 17 is optionally connectedto a switch module 18, which typically has pedal or push buttonswitches. The output of the switch module allows the user to select thelevel of power desired for a given procedure, or to select other modesof operation available to particular medical devices, when the switchmodule is connected to the control voltage means described below.Alternatively, the switches can directly control the power levelprovided to the medical device. The interface board 17 is also attachedto a current control knob or switch 19, a device LED 20 indicatingwhether an attached device is capable of functioning with the powersupply, and a switch LED 21 that indicates that use of the switch module18 is required. Note that other interface boards may be added to thepower board.

[0016]FIG. 3 is a block diagram of the power board system. The powerboard 14 is conceptualized as three circuits: a device identificationcircuit 26, a control voltage circuit 27, and a constant current circuit28. The electrical surgical device 15 is electrically connected to thedevice identification circuit 26 and receives current from the constantcurrent circuit 28. A constant DC power source, V_(cc) (item 29), isprovided to all three circuits 27, 28, and 29, and is operated to supplypower at about +5 volts DC. Note that other circuit blocks may be added,such as a circuit that provides a tone indicating the level of powerrunning through the medical device or a circuit that facilitates the useof additional switches or pedals to control the power output of thepower supply.

[0017]FIG. 4 is a circuit diagram of the device identification circuit26, which includes all three diagrams shown in FIG. 4. The portion ofthe device identification circuit shown in area 35 (comprising the box35 shown in phantom) contains the portion of the identification circuitlocated in the electrical surgical tool. The portion of the ID circuitshown in area 36 (comprising the box 36 shown in phantom) is located inthe power supply box. Nevertheless, the various components of the deviceidentification circuit can be placed in either the electrical surgicaldevice or the power supply box. For example, all of the circuit could beinside the electrical surgical tool or all of the circuit could beplaced inside the power supply box. However, if the identificationresistor, R_(id), is placed inside the power supply box, then means areprovided such that a specific electrical surgical device plugs into acorresponding identification resistor. For example, a different outletin the power supply box can be provided for each electrical surgicaldevice. Alternatively, each electrical surgical device plug can have adifferent pin arrangement that plugs into a single outlet in the powersupply box. In this case, the pin arrangement selects the properidentification resistor.

[0018] The device identification circuit can determine whether anelectrical surgical device is plugged in or plugged in properly, whetherthe device is a device for which the power supply is designed, and whichof a plurality of electrical surgical devices designed for use with thepower supply is electrically connected to the power supply. In addition,the circuit of FIG. 4 constitutes a device identification means (or anelectrical surgical device identification means or a thermal cauterydevice identification means), though the circuit may be varied in manyrespects. For example, the circuit of FIG. 4 is designed to identifythree medical devices, though the circuit could add additional resistorsto the resistor ladder and add additional comparators so that the deviceidentification circuit can identify a plurality of electrical surgicaldevices or other kinds of electrical medical devices. In addition,capacitors can be added or subtracted from the circuit in order tocreate different kinds of filters. Also, the resistive heating elementof the electrical surgical device can comprise the identificationresistor as long as the resistive heating element of each electricalsurgical device has a distinct resistance.

[0019] Referring again to FIG. 4, a voltage V_(CC) is placed across aresistor, R_(id), which is located in the plug of the medical device,and a reference resistor, R_(r), connects to ground. An identifyingvoltage, V_(id), develops across R_(r). Note that V_(id) varies with thevalue of R_(id). R_(id) is set by the manufacturer and is unique to aparticular model of medical device. A capacitor, C_(r), is placed inparallel with the reference resistor and operates as a low pass filter.

[0020] The identifying voltage, V_(id), is sent to a comparator, whichcompares V_(id) to a reference voltage, V_(r). If the identifyingvoltage, V_(id), is greater than the reference voltage, V_(r), then thecomparator (which can be a true comparator or an operational amplifieroperated as a comparator) outputs a “1” signal. If the identifyingvoltage is less than the reference voltage, then the comparator outputsa “0” signal. The output of the comparator is provided to the controlvoltage circuit 27, which generates a control voltage, V_(c). Thecontrol voltage determines, through the constant current circuit 28, theamount of power provided to the medical device.

[0021] The device identification circuit in FIG. 4 is designed to detectthree kinds of medical instruments, each of which has a separateidentifying resistor, R_(id). Thus, the voltage cascade circuit has fourcomparison resistors, R_(c1), R_(c2), R_(c3), and R_(c4), placed in aresistor ladder. The resistor ladder produces a voltage cascadecomprising a series of reference voltages. A reference voltage is takenbetween each of the reference resistors, the reference voltagescomprising V_(r1), V_(r2), and V_(r3). Each reference voltage isprovided to the negative terminal of a distinct comparator; thus, V_(r1)is provided to comparator 37, V_(r2) is provided to comparator 38, andV_(r3) is provided to comparator 39. On the other hand, the sameidentifying voltage, V_(id), is provided to the positive terminal ofeach comparator. The output of each comparator, 40, 41, and 42, isprovided to the control voltage circuit 27.

[0022] A first model of a medical instrument (device A) has anidentifying resistor, R_(id), with the smallest value. In this case theidentifying voltage, V_(id), will be higher than all three of thereference voltages. Thus, all three comparators will output a “1”signal. The fact that all three comparators output a signal iscommunicated through the control voltage circuit 27, which outputs acontrol voltage, V_(c). The constant current circuit 28 then uses thecontrol voltage to control electrical power to device A in an amountappropriate to device A.

[0023] Similarly, a second model of medical instrument (device B) willhave an identifying resistor, R_(id), of medium resistance. In this casethe identifying voltage, V_(id), will be lower than the first referencevoltage, V_(r1), but higher than the other two, V_(r2) and V_(r3). Thus,only comparators 38 and 39 will produce a “1” output. Accordingly, theconstant current circuit 28 will recognize that device B is connected tothe power supply. On the other hand, if a third model of medicalinstrument (device C) is connected to the power supply then V_(id) willbe less than V_(r1) and V_(r2), but greater than V_(r3). In this case,only comparator 39 will report a “1” output and the constant currentcircuit 28 will recognize that device C is connected to the powersupply. However, if R_(id) is not present or does not have the correctvalue, then all of the comparators will output a “0” signal. In thiscase the control voltage will be “0” and then the constant currentcircuit will provide no power to the device. Thus, the power supplyusing the device identification circuit of FIG. 4 will only work withthermal cautery devices A, B, and C.

[0024] The various values of C_(r), R_(r), R_(id), R_(c), V_(r), andV_(id) are set by the manufacturer and can have a wide range of values.In one embodiment V_(cc)=+5V, C_(r)=10 μF, R_(r)=10 KΩ, R_(c1)=15 KΩ,R_(c2)=20 KΩ, R_(c3)=10 KΩ, and R_(c4)=5.1 KΩ. In this case V_(r1)=3.5V,V_(r2)=1.5V, and V_(r3)=0.5V. In addition, there are three thermalcautery devices designed by the manufacturer to operate with the powersupply, the thermal cautery devices having a R_(id) values of 1 KΩ, 10KΩ, and 51 KΩ respectively. Furthermore, V_(id) will have 3 differentvalues, one for each thermal cautery device, as shown in the table ofFIG. 5.

[0025]FIG. 5 is a device identification table showing the specificvalues of the identification resistor, the identification voltage, andthe comparator outputs for the three distinct thermal cautery devicesand a foreign device. The columns in FIG. 5 reflecting comparatoroutputs 40, 41, and 42 show that each thermal cautery device has aunique set of comparator outputs. In the comparator output columns ofFIG. 5, a “1” indicates an output signal of “1” and a “0” indicates anoutput signal of “0”. Note that for each device (table row) V_(r1)=3.5V,V_(r2)=1.5V, and V_(r3)=0.5V

[0026] The table of FIG. 5 shows that when thermal cautery device A,with an R_(id) of 1 KΩ, is plugged into the power supply then V_(id) is4.5V, which is higher than all three of the reference voltages, V_(r1)(3.5V), V_(r2) (1.5V), and V_(r3) (0.5V). Thus, comparators 37, 38, and39 all output a “1” signal and the system then knows that thermalcautery device A is plugged into the power supply. Applying similarlogic, the system can tell if thermal cautery devices B or C are pluggedinto the system. However, if a foreign device is plugged into thesystem, or if no device is plugged into the system, then R_(id) isinfinity and thus V_(id)=0. If V_(id) is 0 then V_(id) is less than allthree values of V_(r); accordingly, all of the comparators will output a“0” signal and the constant current circuit 28 will provide noelectrical power to the thermal cautery device.

[0027] The output of the device identification circuit, 40, 41, and 42,is fed into the input of the control voltage circuit 27. The controlvoltage circuit is a series of logic gates and analog circuits connectedto the comparators and, optionally, to switches in the interface board.The logic gates, analog circuits, and switches constitute a controlvoltage means. The control voltage circuit 27 outputs a control voltage,V_(c), based on the output of the comparators and, optionally, based onthe interface board switches 18. The control voltage that is output bythe control voltage means is unique to a particular electrical surgicaldevice that has been designed to work with the power supply. Theswitches and the control voltage circuit allow the user to select acontrol voltage from a set number of control voltages. The constantcurrent circuit 28 uses the control voltage, V_(c), to determine theamount of current delivered to the thermal cautery device.

[0028]FIG. 6 is a circuit diagram of the constant current circuit 28.The main current path proceeds from V_(cc) (typically +5 volts), throughoutput plug (between terminals 46 and 47 when the terminals areelectrically connected), through a power MOSFET 48 and finally through asense resistor, R_(s), used to sense the amount of current, I_(main),flowing through the main current path. Other kinds of transistors canalso be used, such as a JFET transistor or an NPN transistor (BJTtransistor). A capacitor, 49, is placed between the terminals of theoutput plug and acts as a low pass filter. When current flows throughthe main current path, R_(s) generates a sense voltage, V_(s),proportional to the main current (V_(s)=I_(main×R) _(s)).The circuitprovides the sense voltage, V_(s), to the negative terminal of anoperational amplifier 50 through a low pass filter comprising resistor51 and capacitors 52 and 53. The operational amplifier 50 is alsoconnected to ground and to V_(cc). The positive terminal of theoperational amplifier is connected to the control voltage, V_(c),through a low pass filter comprising capacitor 54. The operationalamplifier compares the control voltage, V_(c), to the sense voltage,V_(s), and generates an output that controls the gate 55 of the powerMOSFET 48. (The MOSFET drain 56 and source 57 are shown forconvenience). The result is that the operational amplifier 50 adjuststhe current flowing through the power MOSFET 48 until the sense voltageis equal to the control voltage (V_(s)=V_(c)). Thus, the constantcurrent circuit 28 maintains the current at a steady level. The amountof current is set by the value of the sense resistor, R_(s). Forexample, if the sense resistor, R_(s)=0.1 Ω and the control voltage,V_(c)=0.1V, then the main current, I_(main)=1.0A.

[0029] The output plug (terminals 46 and 47) is electrically connectedto the medical instrument's resistive heating elements, thus completingthe electrical circuit. Accordingly, the current flowing through themain current path powers the medical instrument reliably and selectably.The circuit of FIG. 6 constitutes a constant current means, though thecircuit can be varied in many respects. For example, the capacitors andresistors can take on different values, may be taken out of the circuit,or other capacitors and resistors may be added to accomplish differentfiltering effects. In addition, the circuit can be similarly modified toprovide different output currents for a given control voltage.

[0030]FIG. 7 is a circuit diagram of an alternate device identificationcircuit. A voltage, V_(cc), is placed across a resistor, R_(id), whichis located in the plug of the electrical surgical tool. R_(id) is set bythe manufacturer and is unique to a particular thermal cautery device. Asecond resistor, 63, is connected to a control resistor, 64, whichitself connects to ground. A control voltage, V_(c), develops acrosscontrol resistor 64 and V_(c) varies with the value of R_(id). Thecontrol voltage is provided to a constant current circuit, such as thatshown in FIG. 5, which provides a constant current to the thermalcautery device. The output current is a function of V_(c) and R_(id)(I_(output)=V_(c)/R_(id)).

[0031]FIG. 8 is a circuit diagram of an alternate device identificationcircuit with switching. Three circuits, similar to the one in FIG. 7,are combined using three different identification resistors, R_(id1),R_(id2), and R_(id3), though resistors 63 and 64 have the same value inall three circuits. In addition, a switch 65 is provided in eachindividual circuit between the second resistor 63 and the controlresistor 64. The switch 65 can be any kind of switch, such as a pushbutton, a pedal, or a knob. Selecting a switch chooses one of thecontrol voltages, V_(c1), V_(c2), or V_(c3), and sends that controlvoltage to a constant current circuit, such as the one shown in FIG. 6.The constant current circuit then provides a constant current to theelectrical surgical tool appropriate to the particular thermal cauterydevice and appropriate to the switch or switch combination selected. Inone embodiment the values of the components are R_(id1)=2.75 KΩ,R_(id2)=3.67 KΩ, R_(id3)=5.5 KΩ, R₆₃=10 KΩ, R₆₄=1 KΩ. Since V=IR then inthis embodiment I_(output)=11 KΩ/R_(id).

[0032] Depending on the design of the constant current circuit, controlvoltage circuit, or other additional circuit, the combination ofswitches can control a variety of variables. For example, an electricalsurgical tool may have one subcomponent that requires power. In thiscase the three switches control whether the device receives a “high”,“medium”, or “low” amount of power. The constant current circuit shownin FIG. 6 can operate with the device identification circuit of FIG. 8to perform this function.

[0033] Alternatively, other control voltage circuits can add additionalcapabilities when used in conjunction with the switch design of FIG. 8.For example, an electrical surgical tool can have three subcomponents,each of which require power. The three switches determine which, if any,of the subcomponents receive power. For other constant current circuitsit is possible to use different combinations of open and closedswitches. For the circuit shown in FIG. 8 there are eight possibleswitch combinations. Each combination of switch positions generates adistinct control voltage that can control different elements or powerlevels of the electrical surgical tool.

[0034] A plurality of switch circuits is also possible. In the case of aelectrical surgical tool with three powered subcomponents, each of whichhaving three power settings, then nine switches can control whichsubcomponent receives a given amount of power (depending on the designof the constant current circuit and control voltage circuits). Inaddition, a plurality of electrical surgical tool can be attached to thecircuit, each electrical surgical tool having a unique identifyingresistor. In this case the plurality of switches determine which, ifany, of the devices are “on”. Finally, a plurality of switches can beprovided on a circuit that accommodates multiple devices, each devicehaving multiple powered subcomponents, each powered subcomponent havingmultiple power levels, and wherein different combinations of switchpositions control different aspects of the device.

[0035] Although the methods, devices, and circuits are described inrelation to electrical surgical tools, the same methods, devices, andcircuits can be used with other kinds electrical devices where deviceidentification is desired. For example, electrical surgical tools usingDC, AC, or RF power can use the device identification methods describedabove. Electrical surgical tools useable with the device identificationcircuit also include ablation devices, thermal ligation devices, thermalcautery devices, electrocautery devices and other kinds electro-medicalinstruments. Thus, while the preferred embodiments of the devices andmethods have been described in reference to the environment in whichthey were developed, they are merely illustrative of the principles ofthe inventions. Other embodiments and configurations may be devisedwithout departing from the spirit of the inventions and the scope of theappended claims.

I claim:
 1. A power supply capable of identifying an electrical surgicaltool, the power supply comprising: an AC to DC converter; and a powerboard adapted to receive power from the AC to DC converter, said powerboard comprising an electrical surgical device identification means foridentifying which of a plurality of electrical surgical devices areelectrically connected to the power supply, and wherein said pluralityof electrical surgical devices are designed to operate with the powersupply.
 2. The power supply of claim 1 wherein the electrical surgicaldevice identification means for identifying the electrical surgicaldevice has an output, and wherein the power supply further comprises acontrol voltage means for generating a control voltage, said means forgenerating a control voltage adapted to receive the output of the meansfor identifying an electrical surgical device, and wherein the means forgenerating a control voltage is capable of outputting a control voltagethat is unique to the specific electrical surgical device electricallywhen connected to the power supply.
 3. The power supply of claim 2further comprising an interface board electrically connected to thepower board, said interface board having switches and said switcheshaving an output, wherein the output of the switches is capable ofcontrolling the power provided to the electrical surgical tool when theoutput of the switches is provided to the means for generating a controlvoltage.
 4. A power supply capable of identifying an electrical surgicaltool, the power supply comprising: an AC to DC converter; a power boardadapted to receive power from the AC to DC converter, said power boardcomprising an electrical surgical device identification means foridentifying an electrical surgical device, said means for identifying anelectrical surgical device being capable of identifying which of aplurality of electrical surgical devices are electrically connected tothe power supply; wherein the means for identifying an electricalsurgical device is further capable of determining whether an electricalsurgical device electrically connected to the power supply is designedto operate with the power supply.
 5. An electrical circuit capable ofidentifying an electrical surgical tool, said electrical circuitcomprising: a power source; an identification resistor disposed in theplug of the electrical surgical tool, said identification resistorcapable of receiving power from the power source; a reference resistorplaced in series with the identification resistor, and electricallyconnected to ground, such that an identifying voltage develops acrossthe reference resistor when power is applied to the electrical circuit;a comparison resistor electrically connected to the power source and toground, wherein a reference voltage develops across the comparisonresistor when power is applied to the electrical circuit; a comparator,wherein a positive terminal of the comparator is electrically connectedto the identifying voltage and the negative terminal of the comparatoris electrically connected to the reference voltage; wherein thecomparator produces an output signal if the identifying voltage ishigher than the reference voltage.
 6. The electrical circuit of claim 5further comprising a capacitor placed in parallel with the referenceresistor.
 7. The electrical circuit of claim 5 wherein theidentification resistor is chosen from the group consisting of about 1KΩ, about 10 KΩ, and about 51 KΩ.
 8. An electrical circuit capable ofidentifying one of a plurality of electrical surgical tools, saidelectrical circuit comprising: a power source; an identificationresistor, wherein the identification resistor comprises a distinctresistor disposed in the plug of each of the plurality of electricalsurgical tools and wherein the resistor of one electrical surgical toolhas a distinct resistance from the resistor of all of the otherelectrical surgical tools, and wherein the identification resistor iscapable of receiving power from the power source; a reference resistorplaced in series with the identification resistor, and electricallyconnected to ground, such that an identifying voltage develops acrossthe reference resistor when power is applied to the electrical circuit;a resistor ladder comprising a plurality of comparison resistors, saidresistor ladder electrically connected to the power source and toground, wherein a corresponding plurality of reference voltages developsacross the resistor ladder when power is applied to the electricalcircuit; a plurality of comparators, wherein the positive terminal ofeach of the plurality comparators is electrically connected to theidentifying voltage and the negative terminal of each of the pluralityof comparators is electrically connected to one corresponding referencevoltage; wherein each of the plurality of comparators produces an outputsignal if the identifying voltage is higher than the correspondingreference voltage.
 9. The electrical circuit of claim 8 wherein theplurality of electrical surgical tools comprises three electricalsurgical tools and wherein the individual identification resistor of thethree electrical surgical tools have values of about 1 KΩ, about 10 KΩ,and about 51 KΩ respectively.
 10. The electrical circuit of claim 8further comprising a capacitor placed in parallel with the referenceresistor.
 11. A device identification circuit capable of providing aconstant current only to a specific thermal cautery device, said deviceidentification circuit comprising: a power source; a resistive elementwithin the thermal cautery device, said resistive element electricallyconnected to the power source and to the drain of a power MOSFET; asense resistor electrically connected to the source of the power MOSFETand to ground, wherein a sense voltage develops across the senseresistor when power is applied to the circuit; an operational amplifier,wherein the output of the operational amplifier is electricallyconnected to the gate of the power MOSFET, wherein the negative terminalof the operational amplifier is electrically connected to the sensevoltage, and wherein the positive terminal of the operational amplifieris electrically connected to a control voltage such that the circuitwill adjust the current until the sense voltage equals the controlvoltage; wherein the control voltage is dependent on the output of adevice identification means for identifying a thermal cautery device,said means for identifying a thermal cautery device designed to operatewith a power supply having the device identification circuit.
 12. Anelectrical circuit capable of identifying one of a plurality ofelectrical surgical tools and also providing a constant current to oneof the plurality of electrical surgical tools, said electrical circuitcomprising: a power source; an identification resistor, wherein theidentification resistor comprises a distinct resistor disposed in a plugof each of the plurality of electrical surgical tools and wherein aresistor of one electrical surgical tool has a distinct resistance fromthe resistor of all of the other electrical surgical tools, and whereinthe identification resistor is capable of receiving power from the powersource; a reference resistor placed in series with the identificationresistor, and electrically connected to ground, such that an identifyingvoltage develops across the reference resistor when power is applied tothe electrical circuit; a resistor ladder comprising a plurality ofcomparison resistors, said resistor ladder electrically connected to thepower source and to ground, wherein a corresponding plurality ofreference voltages develops across the resistor ladder when power isapplied to the electrical circuit; a plurality of comparators, whereinthe positive terminal of all of the plurality comparators iselectrically connected to the identifying voltage and the negativeterminal of each of the plurality of comparators is electricallyconnected to one corresponding reference voltage; wherein each of theplurality of comparators produces an output signal if the identifyingvoltage is higher than the corresponding reference voltage, and whereinthe set of outputs of the plurality of comparators is capable ofidentifying which of the plurality of electrical surgical tools isplugged into the circuit; at least one resistive heating element withineach of the plurality of electrical surgical tools, said at least oneresistive heating element electrically connected to the source ofelectrical power and to the drain of a power MOSFET; a sense resistorelectrically connected to the source of the power MOSFET and to ground,wherein a sense voltage develops across the sense resistor when power isapplied to the circuit; an operational amplifier, wherein the output ofthe operational amplifier is electrically connected to the gate of thepower MOSFET, wherein the negative terminal of the operational amplifieris electrically connected to the sense voltage, and wherein the positiveterminal of the operational amplifier is electrically connected to acontrol voltage such that the circuit will adjust the current throughthe at least one resistive heating element until the sense voltageequals the control voltage; wherein the control voltage is dependent onthe set of outputs of the plurality of comparators.
 13. A system forperforming thermal cautery comprising: at least one thermal cauterydevice, wherein each of the at least one thermal cautery devicescomprises a resistive heating element; and a power supply capable ofproviding power to the at least one thermal cautery device, wherein thepower supply further comprises a thermal cautery device identificationmeans for identifying a thermal cautery device, said means foridentifying a thermal cautery device capable of identifying which of theat least one of the thermal cautery devices are electrically connectedto the power supply, and wherein each of the at least one thermalcautery devices are designed to operate with the power supply.
 14. Asystem for performing thermal cautery comprising: at least one thermalcautery device, wherein each of the at least one thermal cautery devicescomprises a resistive heating element; and a power supply capable ofproviding power to the at least one thermal cautery device, wherein thepower supply further comprises a thermal cautery device identificationmeans for identifying a thermal cautery device, said means foridentifying a thermal cautery device being capable of identifying whichof the at least one of the thermal cautery devices are electricallyconnected to the power supply, and wherein the means for identifying athermal cautery device is further capable of determining whether athermal cautery device electrically connected to the power supply isdesigned to operate with the power supply.